Electron multiplier



June 27, 1950 H. w. G. SALINGER 2,512,683

ELECTRON MULTIPLIER Filed oct. 7, 194e FIG.2

INVENTOR HANS W G. SALINGER ATTORNEY Patented June 27, 1950 UNITED srArEs rerum OFFICE ELECTRON MULTIPLIER Hans W. G. Salinger, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application octobery 7, 194s, seri-ar No. 701,728 cclaims. (c1. 25o- 175) l This invention relates to electron multipliers and particularly to a high amplification static multiplier which requires a minimum of space. Electron multipliers are usually classified as either static multipliers or dynamic multipliers. In a dynamic multiplier an electron beam to be multiplied impacts repeatedly the same secondary electron emiss'ive surface whereby multiplication of the electron beam is effected. A static electron multiplier is provided with a plurality of secondary electron emissive stages upon each of which an electron beam impacts once to multiply the primary electron beam. The present invention is directed to a static multiplier of the type where successive multiplying stages are energized by increasing steady positive potentials.

The multiply-ing stages of a static'multiplier must he arranged in such a manner that the elec-` tron beam may be directed from each stage to a succeeding stage. In a conventional static mul-V tiplier the stagesare either arranged in a straightl line, the electron beam being directed from one stage to the succeeding stage by the combined action of an electromagnetic and an electrostatic eld. Alternatively it has been suggested to arrange the multiplying stages so that -the electron paths between successive stages form an angular path and the electrons progress in a single direction :from stage to stage. A multiplier of this type requires only electrostatic elds for directing the electrons from stage to stage. When a large number of multiplying stages is required, a conventional electron multiplier requires a comparatively large space in view of the conventional arrangement oi the multiplying. stages. It is therefore desirable to provide an electron multiplier where a large number of stages may be provided in a minimum of space.

It is an object of the present invention, therefore, to provide a novel high amplification electron multiplier which requires a minimum of space even for a' large number of .multiplying stages.

In accordance with theinvention there is pro-'il vided an electron multiplier comprising a plurality of secondary electronv emissive stages.A arranged along a closedsurface and a perforated accelerating electrode provided within the stages.I

Means are provided for developing primary elec-..

2 cessive stages and means are arranged for sup,- plying a potential to the accelerating electrode that is more positive than that of any one of the stages. Finally means are provided for collecting the electrons. liberated from the last oneL ofl the stages.

For a better understanding oi the invention, together with other and further objects thereof, reference -is made to the following: description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In thev accompanying drawing, Fig. l is a Schematic diagram of a three stage electron multiplier embodying the present invention, While Fig. 2 is` a schematic diagram of a ten stage` electron multiplier in accordance with the invention.

Referring to Fig. 1, there is illustrated a three stage electron multiplier I embodying the present invention. Electron multiplier I comprises cathode 2, which may be indirectly vheated as indi`r cated., control grid 3, successive secondary electron emissive stages 4, 5 and Ii and collector electrode 'I all provided in evacuated envelope 8. Per-A forated accelerating electrodev I0 is provided With. in multiplying stages 4, 5 and E and may consist of a grid. As clearly shown in Fig. 1, accelerating electrode l0 is common to all multiplying. stages and extends substantially parallel to each` multi` plying stage 4, 5 and I5y and to cathode 2. Collector electrode 'I may be electrically insulated from accelerating electrode I0.

For the purpose of supplying operating potentials to the electrodes of multiplier i there may be provided a suitable voltage source such, fory example,l asvbattery I2 having its terminals connected across voltage divider I3., The positive terminal of battery I2 may be groundedas. shown. By means oiwtaps i4, I5 and I6 on voltage divider I3 successive lmultiplying stages 4 5 and 6, are maintained at` increasing positive potentials. By way of example, each stage may have a positive potentialfof 200 volts with respectto the previous stage. Cathode 2 is. supplied through tap l'I. on voltage divider I3 with such a potential thatthe nrsty multiplying stage 4 is positive againstcath.- ode `2. Bymeansof tap` I8 control grid 3 may be maintained at a potential that is negative with respect to that of cathode 2.

The input signal @tamed from input terminals 2li may be impressed through input transformer yZI. between control grid 3 and cathode 2'. Accelerating electrode I0 is. maintained at the. most positive potential, which may be ther groundY potential., Collector electrode-1 is conllveltedvto ground through load resistor 22 across which the output signal may be derived from output lead 23.

The electron multiplier of Fig. l operates as follows. Accelerating electrode IIJ which is swbstantially closed forms a Faraday or equipotential space. The primary electron beam developed by cathode 2 is modulated in accordance with the input signal by control grid 3. The modulated primary electron beam is now attracted by accelerating electrode I and directed toward the iirst multiplying stage 4. The electron beam accordingly traverses a eldless space Within accelerating electrode IIl. In this fieldless space the electron beam is shielded from the electrostatic fields developed by the other elec- 4 the same manner as electron multiplier I. The electron paths from 'cathode 2 to collector electrode l have been indicated lby broken line 43. Successive multiplying stages are again arranged in such a manner that substantially all electrons liberated from one stage are collected by the succeeding stage.

The electron stages of the multiplier of the invention are arranged in a plane and along a closed surface which may assume many different forms, such as those illustrated in Figs. l. and 2. It is also feasible to arrange the multiplying stages along a spiral extending through a full revolution so that the electrons from each trodes of the multiplier and `therefore travels in a straight path. After leaving the space within accelerating electrode IIJ, the modulated primary electron beam is decelerated and impacts multiplying stage i as indicated by dotted line 25. As 'shown by lin'e 25, the=decele`ration of the electron beam causes a deflection thereof, and the multiplying stages must be positioned accordingly as illustrated to receive the electron beam. It will therefore be seen that multipying stage 4= isv arranged substantially opposite cathode 2 with respect to accelerating electrode I.

The secondary electrons liberated from multiplying stage 4 are again attracted by accelerating electrode I0 and traverse its iieldless space to be decelerated again before rea-ching the succeeding multiplying stage 5. Multiplying stages 4,` 5 and 6 are arranged in a plane and along a closed surface. Each multiplying stage 4, 5 and 6 is arranged opposite the succeeding stage and at such an angle that the electrons liberated from any multiplying stage 4, 5 or 6 are directed to the succeeding stage or to collector electrode 1, as the case may be, in such a manner that the electron paths between every two successive stages intersect each other within accelerating electrode IIJ. The electron lbeam lib eratd from any multiplying stage such as 4, 5 or 5 forms substantially a right angle with that stage, While the succeeding stage must be arranged' in such a manner that substantially all electrons liberated from the preceding stage are collected thereby. Collector electrode 'I may be arranged-substantially parallel with lastmultiplying stage 6.

The multiplier of the invention thus provides a very compact structure wherein space charge limitations are minimized in view of the action of accelerating electrode I0.

Referring now to Fig. 2, in which like components are designated y by the vsame reference numerals as Wereused in Fig. Lthere is illustrated'a ten stage electron multiplier 30 which operates ,in substantially'the same manner as the multiplier of `Fig. l. The multiplier of Fig. 2 comprises 'cathode 2, control grid 3 and ten successive multiplying stages 3l', 32, 33, 34, 35, 36,31, 38, 39 and 40. Accelerating electrode I 0 is again provided withir'r multiplying stages 3l to`4Il andI may be electrically connected to collector electrode '1. Accelerating electrode IIJ preferably extends substantially parallel to each multiplying stage 3l to 4D and to cathode 2. By means of suitable taps on voltage divider I3, energized from battery I2, operating potentials may be supplied to cathode'2, control grid 3, multiplying stages 3I to 40 and accelerating electrode I0 as explained hereinbefore. l

" The' electron multiplier of-Fig. 2 operates in stage are directed to the succeeding stage. It Will be understood that a certain fraction of the electrons traveling between the multiplying .stages is intercepted by accelerating electrode l0. However, when accelerating electrode 2 is electrically -connected to collector electrode '1, as shown in Fig. 2, the electrons collected by accelerating electrode il) will be added to the output signal. It will furthermore be evident that the high positive potential of accelerating electrode I0 will substantially prevent the formation o! f space charges.

Cathode 2 of either multiplier I or of multiplier 30 need not be a thermionic cathode but may be a photocathode as is conventional. In that case the primary beam of photoelectrons is preferably modulated by varying the intensity of the light falling on the photocathode. The multiplier of the invention may therefore be used with advantage as a photocell multiplier.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is: Y

1. An amplifier system comprising an envelope enclosing a substantially continuous, electron permeable, accelerating electrode enclosing a space within said envelope, means mounted outside said space and said electrode for emitting electrons along a path through said electrode and across said space, a plurality of secondary emissive electrodes mounted in spaced relation outside said space and around said accelerating electrode, one of said emissive electrodes being mounted in the path of said emitted electrons for receiving said electrons and emitting secondary electrons in response thereto through said accelerating electrode and toward a second one of said emissive electrodes on the opposite side of said accelerating electrode along a path co-planar with said first-mentioned path, a further electrode mounted outside said space and on the opposite side of said accelerating electrode with respect to said second one of said emissive electrodes, said second one of said emissive electrodes being mounted in the 4path of said secondary electrons for receiving said secondary electrons and emitting other secondary electrons in response thereto through said accelerating electrode toward said further electrode along a path co-planar with said other paths and intersecting said first-mentioned path, a source of potentials electrodes, said accelerating electrode and said further electrode.

2. An amplifier system according to claim 1 wherein said further electrode is a collector electrode.

3. An amplier system according to claim 1 wherein said further electrode is a secondary emissive electrode mounted outside said space and said accelerating electrode for receiving secondary electrons and emitting other secondary electrons in response thereto through said accelerating electrode along a path co-planar with said other paths and intersecting said rst and second mentioned paths, said system further comprising within said envelope a further electrode mounted in the path of the electrons emitted by said last-mentioned secondary emissive electrode and means for positively biassing said last-mentioned further electrode with respect to said emitting means.

4. An amplifier system according to claim 1 further comprising a control electrode mounted within said envelope between said emitting means and said accelerating electrode and means for coupling control signals to said control electrode.

5. An amplier system comprising an envelope enclosing an electron emitting cathode, a first secondary emissive electrode mounted in the path of the electrons emitted by said cathode and in spaced relation to said cathode, a second secondary emissive electrode mounted on one side of said path and in spaced relation to said emissive electrode and said cathode, a further electrode mounted on the other side of said path and in spaced relation to said electrodes and said cathode, the distance between parallel planes normal to said path and intersecting said cathode and one of said two last-mentioned electrodes being less than the distance between similar planes intersecting said cathode and said first electrode, said first electrode having a secondary emissive surface positioned to receive electrons from said cathode and to emit secondary electrons in response thereto along a path co-planar with said rst-mentioned path and extending toward said second electrode and said second electrode having a secondary emissive surface positioned to receive electrons from said first electrode and to emit secondary electrons in response thereto along a path coplanar with said other paths, and extending toward said further electrode, and means for directing said electrons along said paths comprising an accelerating electrode amounted adjacent said cathode and said electrodes and across the paths of said electrons, a source of potential having positive and negative portions, means for connecting the negative portion to said cathode and Kia means for connecting the positive portion to said electrodes.

6. A n amplifier system comprising an envelope enclosing a substantially continuous, electron permeable, accelerating electrode enclosing a space within said envelope, means mounted outside said space and said electrode for emitting electrons along a path through said electrode and across said space, a plurality of secondary emissive electrodes mounted in spaced relation outside said space and around said accelerating electrode, one of said emissive electrodes being mounted in the path of said emitted electrons for receiving said electrons and emitting secondary electrons in response thereto through said accelerating electrode and toward a second one of said emissive electrodes on the opposite side of said accelerating electrode along a path coplanar with said first-mentioned path, said second one of said emissive electrodes being mounted in the path of said secondary electrons for receiving said secondary electrons and emitting other secondary electrons in response thereto through said accelerating electrode toward a third one of said emissive electrodes on 'the opposite side of said accelerating electrode along a path co-planar with said other paths and intersecting said rst-mentioned path and said third one of said secondary emissive electrodes being mounted in the path of the secondary electrons emitted from said second one of said emissive electrodes for receiving said last-mentioned secondary electrons and emitting other secondary electrons in response thereto through said accelerating electrode along a path co-planu ar with said other paths and intersecting said first-mentioned path and the path of the secondary electrons of said one electrode, a collector electrode mounted in the path of the secondary electrons emitted from said third one of said emissive electrodes, means for biassing each emissive electrode at a higher positive potential with respect to its preceding emissive electrode and with respect to said emitting means and means for positively biassing said accelerating electrode and said collector electrode with respect to said emissive electrodes.

HANS W. G. SALINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,102,045 Thomas Dec. 14, 193'? 2,157,529 Drewell May 9, 1939 2,260,613 Farnsworth Oct. 28, 1941 

